1. Field of the Invention
The present invention pertains to photolithography.
2. Background Art
There are various photolithographic or microlithographic techniques used in the manufacture of very fine patterns in metals, insulators and semiconductors (i.e., devices). In the photolithographic or microlithographic process, a pattern (e.g., a circuit pattern) contained on a reticle is projected (i.e., imaged) onto a wafer. A wafer is typically a photoresistive substrate that is further processed to form a device or devices.
As feature size requirements continue to shrink, the use of phase-shifting reticles has increased. Phase-shifting reticles increase the effective resolution of a lithographic system. The use of phase-shift techniques typically requires the exposure of the same field or area on a wafer first with a phase-shift reticle and then with a trim reticle. The trim reticle can differ from the phase-shift reticle depending on the implementation.
Techniques such as this two-step imaging can create alignment problems. They also can reduce overall wafer throughput of the system (i.e., the system is slowed because each wafer needs to be exposed twice). As each reticle is set for exposure on a given wafer, the precision alignment process consumes additional time and often reduces the efficiency and yield of the system.
What is needed is a method and system for exposing the same field with at least two different reticles simultaneously. Furthermore, what is needed is a method and system for exposing the same field with at least two different reticles simultaneously such that alignment and calibration problems can be prevented.
The present invention provides a method and system that meet the above-stated needs. The method and system of the present invention produce two reticle images side-by-side in the exit pupil of the projection optics of an exposure and/or reduction system.
In one embodiment, the exposure system is a step-and-scan wafer exposure system. In such an embodiment, the scanning action of the exposure tool effectively superimposes the two images during the exposure of the wafer. Thus, each image exposes the photoresist as the wafer is scanned through the image field in a synchronous manner with the scanning of the reticles. In other words, the image scanning is synchronized so that the two required reticle images are superimposed. In an additional embodiment of the present invention, the system can create the two images to be independently focused and finely aligned.
In one embodiment of the present invention, the system projects two images of illuminated slits from two separate reticles mounted on a scanning stage.
In an alternative embodiment, the system projects two images of illuminated slits from two separate locations on a single reticle mounted on a scanning stage.
Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.